Differential detection of ultrasound-modulated light for deep tissue imaging

Abstract

Optical imaging has been recognized as an essential imaging technique for biomedical research because it provides high-resolution(~1um) images and abundant biochemical information. However, the imaging depth of optical techniques is typically shallow(<1 mm) due to the strong scattering properties of biological tissues. Utilizing the ultrasound-light interaction is an effective way to overcome this optical depth limit caused by scattering. Ultrasound can penetrate biological tissues up to several centimeters without distortion and can modulate the frequency of light. To date, the ultrasonic coupled optical microscopy has been implemented by observing the 1st order modulated light waves of which frequency is exactly modulated by the ultrasonic frequency. However, the measurement efficiency of 1st order detection method is significantly low and the imaging resolution is determined by the size of the ultrasound itself. In this study, a new ultrasonic modulated light measurement method, differential detection method is proposed and the operating principle of the differential acoustic light measurement method is explained based on the Raman-Nath theory. In addition, we directly visualized a focused ultrasound by combining acousto-optic detection and imaging techniques, so that it was experimentally demonstrated that differential detection is feasible and quantitative analysis of the performance of the conventional 1st order detection and differential detection was performed.